Preliminary Study On Reconstruction Mechanism In Periodental Tissue Of Rats With Occlusal Trauma

Background:Occlusal trauma is due to abnormal occlusion or bite force which result in damage of periodontal system.Under normal circumstances, the bite force of periodontal tissue can produce positive stimulus, while abnormal bite can cause periodontal tissue pathological damage. In the clinical common occlusal trauma or improper orthodontic force can lead to the root absorption and gomphiasis.In the periodontal ligament,collagen fibers keep reconstruction.The reconstruction is accomplished through fibroblasts collagen synthesis by fibroblast and degradation of collagen. Existing literatures reported any damage to the fiber cell function can lead to loss of the support tissues. The periodontal tissue reconstruction process is complex, including insulin-like growth factor (IGF) and osteoclasts closely related to the reconstruction process.Objective:Through the establishment of animal model of rat molar experimental occlusal trauma, to observe the morphology of collagen fibers, insulin-like growth factor (IGF-I) expression and changes of osteoclast before and after the removal of the stimulation factors.The objective of the study is to discusses the pathogenesis of traumatic occlusion,the pathological process and the recovery process, to provide experimental basis of possibility and methods for clinical intervention.Methods:3 months oldmale Wistar rats, weighing 250—280g, no tooth decay and parodontopathy.They were grouped randomly to five groups. The control group includes 5 rats.The experimental groups respectively observed 1 week,3 weeks,4 weeks and and 2 weeks after traumatic occlusion removal for 2 weeks. Each group has 5 rats.After anesthesia and disinfection, experimental rats bond cobalt-chromium metal 3/4 crown in mandible on the right side of the first molar, higher than occlusal surface 0.8 mm.When reached the observation point,the metal crown were removed.After cardiac perfusion,the target area were made to slice which thickness is 5μm. HE straining to observe the changes of periodontal tissue;Immunohistochemical stained of IGF-I to observe the change;Strained with TRACP and immunohistochemical stained of CK to observe number and activity of change of osteoclast.Use ImagePro-Plus6.0 software to calculate the average optical density value of IGF-I and CK and the number of TRACP in random field of vision.Use Graphpad Prism.6.x.C statistical software for data analysis.Results:1 observation of experimental animalsRats with 1w occlusal trauma were aggressive and bad temper. Rats with 3 w and 4 w were gradually docile,hypokinesia and underreaction. Average body mass growth of rats with occlusal trauma 1 month was reduced 30g, while the hair of rats was tanglesome, a little yellow and poor in lustrousness but smooth, lustrous in the control group.2 HE Staining and histological observatioControl group:The periodontal ligament fibers arrange were neat, and the epithelial attachment to the CEJ.Occlusal trauma group:The slightly disorder of periodontal ligament was found.The trauma in 4-week group is the most serious at the same time the alveolar bone was obvious absorbed.In trauma removal group the vessel dilation can be found.3 IGF-I expression changesControl group:The expressions of IGF-I expressed in periodontal fibroblast and alveolar bone.Occlusal trauma group:The expression of IGF-I in periodontal tissue increase gradually. In the 4-week group, it reached to the maximum. In trauma removal group, the main positive expressions lie in alveolar bone.Each experimental group is statistically significant with the control group (P<0.05).4 osteoclast TRACP in changeControl group:A small amount of expression in the periodontal ligament and alveolar bone at the junction.Occlusal trauma group:TRACP in 1w group was weakly positive expression in the periodontal tissue, while mainly expressed in the border of alveolar bone; 3w group of periodontal tissue is staining positive reaction enhancement; 4w group of alveolar bone expresses a large number of osteoclast, strongly positive expression in bone resorption pit;Compared with 3w,4w group, the removal group has a slightly less positive expression.Osteoblasts can be seen in the resorption pits.Between each experimental group and the control group p<0.01,the control group and experimental group was statistically significant.5 osteoclast CK changesControl group:accidentally visible CK expression positive of osteoclastExperimental group:1w group is a small amount of CK positive expression in osteoclasts; 3w group is mainly in the neighboring periodontal alveolar bone; A large number of positive osteoclasts is observed in 4w group;osteoclast positive abates in removal trauma group while tissue repaired can be found.The control group and 1w,3w,4w group are statistical significance. Conclusion:1 Occlusal trauma can cause pathological change of periodontal tissue in rats, such as periodontal membrane broadening, periodontal fiber disordered and angiectasis.The longer, the pathological change, the more obvious.2 Remove the trauma is salutary to the repair of periodontal tissue.3 IGF-I may take part in the rebuilding procedure in rats before and after occlusal trauma removal.4 Occlusal trauma can induce osteoclast differentiation and cause alveolar bone destruction.